Key subunit interfaces for structures of BbDHFR-TS. Top left, arginine side chains from the opposite TS subunit (yellow) directly bind the terminal dUMP phosphate in the active site of one protomer (violet). Top right, the linker region from one protomer (gray) fits into a hydrophobic groove created by DHFR from the opposite protomer (green). Bottom, binding surface between the DHFR (pink), TS (yellow) and linker (gray) regions of protomer B of apo BbDHFR-TS, with labels for hydrogen-bonding residues. All distances are measured in Å. These figures were created using PDB entries 3i3r
with PyMOL (DeLano, 2002).